/*P:050 Lguest guests use a very simple method to describe devices. It's a * series of device descriptors contained just above the top of normal * memory. * * We use the standard "virtio" device infrastructure, which provides us with a * console, a network and a block driver. Each one expects some configuration * information and a "virtqueue" mechanism to send and receive data. :*/ #include #include #include #include #include #include #include #include #include #include #include /* The pointer to our (page) of device descriptions. */ static void *lguest_devices; /* Unique numbering for lguest devices. */ static unsigned int dev_index; /* For Guests, device memory can be used as normal memory, so we cast away the * __iomem to quieten sparse. */ static inline void *lguest_map(unsigned long phys_addr, unsigned long pages) { return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages); } static inline void lguest_unmap(void *addr) { iounmap((__force void __iomem *)addr); } /*D:100 Each lguest device is just a virtio device plus a pointer to its entry * in the lguest_devices page. */ struct lguest_device { struct virtio_device vdev; /* The entry in the lguest_devices page for this device. */ struct lguest_device_desc *desc; }; /* Since the virtio infrastructure hands us a pointer to the virtio_device all * the time, it helps to have a curt macro to get a pointer to the struct * lguest_device it's enclosed in. */ #define to_lgdev(vdev) container_of(vdev, struct lguest_device, vdev) /*D:130 * Device configurations * * The configuration information for a device consists of a series of fields. * We don't really care what they are: the Launcher set them up, and the driver * will look at them during setup. * * For us these fields come immediately after that device's descriptor in the * lguest_devices page. * * Each field starts with a "type" byte, a "length" byte, then that number of * bytes of configuration information. The device descriptor tells us the * total configuration length so we know when we've reached the last field. */ /* type + length bytes */ #define FHDR_LEN 2 /* This finds the first field of a given type for a device's configuration. */ static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len) { struct lguest_device_desc *desc = to_lgdev(vdev)->desc; int i; for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) { if (desc->config[i] == type) { /* Mark it used, so Host can know we looked at it, and * also so we won't find the same one twice. */ desc->config[i] |= 0x80; /* Remember, the second byte is the length. */ *len = desc->config[i+1]; /* We return a pointer to the field header. */ return desc->config + i; } } /* Not found: return NULL for failure. */ return NULL; } /* Once they've found a field, getting a copy of it is easy. */ static void lg_get(struct virtio_device *vdev, void *token, void *buf, unsigned len) { /* Check they didn't ask for more than the length of the field! */ BUG_ON(len > ((u8 *)token)[1]); memcpy(buf, token + FHDR_LEN, len); } /* Setting the contents is also trivial. */ static void lg_set(struct virtio_device *vdev, void *token, const void *buf, unsigned len) { BUG_ON(len > ((u8 *)token)[1]); memcpy(token + FHDR_LEN, buf, len); } /* The operations to get and set the status word just access the status field * of the device descriptor. */ static u8 lg_get_status(struct virtio_device *vdev) { return to_lgdev(vdev)->desc->status; } static void lg_set_status(struct virtio_device *vdev, u8 status) { to_lgdev(vdev)->desc->status = status; } /* * Virtqueues * * The other piece of infrastructure virtio needs is a "virtqueue": a way of * the Guest device registering buffers for the other side to read from or * write into (ie. send and receive buffers). Each device can have multiple * virtqueues: for example the console driver uses one queue for sending and * another for receiving. * * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue * already exists in virtio_ring.c. We just need to connect it up. * * We start with the information we need to keep about each virtqueue. */ /*D:140 This is the information we remember about each virtqueue. */ struct lguest_vq_info { /* A copy of the information contained in the device config. */ struct lguest_vqconfig config; /* The address where we mapped the virtio ring, so we can unmap it. */ void *pages; }; /* When the virtio_ring code wants to prod the Host, it calls us here and we * make a hypercall. We hand the page number of the virtqueue so the Host * knows which virtqueue we're talking about. */ static void lg_notify(struct virtqueue *vq) { /* We store our virtqueue information in the "priv" pointer of the * virtqueue structure. */ struct lguest_vq_info *lvq = vq->priv; hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0); } /* This routine finds the first virtqueue described in the configuration of * this device and sets it up. * * This is kind of an ugly duckling. It'd be nicer to have a standard * representation of a virtqueue in the configuration space, but it seems that * everyone wants to do it differently. The KVM coders want the Guest to * allocate its own pages and tell the Host where they are, but for lguest it's * simpler for the Host to simply tell us where the pages are. * * So we provide devices with a "find virtqueue and set it up" function. */ static struct virtqueue *lg_find_vq(struct virtio_device *vdev, bool (*callback)(struct virtqueue *vq)) { struct lguest_vq_info *lvq; struct virtqueue *vq; unsigned int len; void *token; int err; /* Look for a field of the correct type to mark a virtqueue. Note that * if this succeeds, then the type will be changed so it won't be found * again, and future lg_find_vq() calls will find the next * virtqueue (if any). */ token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len); if (!token) return ERR_PTR(-ENOENT); lvq = kmalloc(sizeof(*lvq), GFP_KERNEL); if (!lvq) return ERR_PTR(-ENOMEM); /* Note: we could use a configuration space inside here, just like we * do for the device. This would allow expansion in future, because * our configuration system is designed to be expansible. But this is * way easier. */ if (len != sizeof(lvq->config)) { dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len); err = -EIO; goto free_lvq; } /* Make a copy of the "struct lguest_vqconfig" field. We need a copy * because the config space might not be aligned correctly. */ vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config)); /* Figure out how many pages the ring will take, and map that memory */ lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT, DIV_ROUND_UP(vring_size(lvq->config.num), PAGE_SIZE)); if (!lvq->pages) { err = -ENOMEM; goto free_lvq; } /* OK, tell virtio_ring.c to set up a virtqueue now we know its size * and we've got a pointer to its pages. */ vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages, lg_notify, callback); if (!vq) { err = -ENOMEM; goto unmap; } /* Tell the interrupt for this virtqueue to go to the virtio_ring * interrupt handler. */ /* FIXME: We used to have a flag for the Host to tell us we could use * the interrupt as a source of randomness: it'd be nice to have that * back.. */ err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED, vdev->dev.bus_id, vq); if (err) goto destroy_vring; /* Last of all we hook up our 'struct lguest_vq_info" to the * virtqueue's priv pointer. */ vq->priv = lvq; return vq; destroy_vring: vring_del_virtqueue(vq); unmap: lguest_unmap(lvq->pages); free_lvq: kfree(lvq); return ERR_PTR(err); } /*:*/ /* Cleaning up a virtqueue is easy */ static void lg_del_vq(struct virtqueue *vq) { struct lguest_vq_info *lvq = vq->priv; /* Tell virtio_ring.c to free the virtqueue. */ vring_del_virtqueue(vq); /* Unmap the pages containing the ring. */ lguest_unmap(lvq->pages); /* Free our own queue information. */ kfree(lvq); } /* The ops structure which hooks everything together. */ static struct virtio_config_ops lguest_config_ops = { .find = lg_find, .get = lg_get, .set = lg_set, .get_status = lg_get_status, .set_status = lg_set_status, .find_vq = lg_find_vq, .del_vq = lg_del_vq, }; /* The root device for the lguest virtio devices. This makes them appear as * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */ static struct device lguest_root = { .parent = NULL, .bus_id = "lguest", }; /*D:120 This is the core of the lguest bus: actually adding a new device. * It's a separate function because it's neater that way, and because an * earlier version of the code supported hotplug and unplug. They were removed * early on because they were never used. * * As Andrew Tridgell says, "Untested code is buggy code". * * It's worth reading this carefully: we start with a pointer to the new device * descriptor in the "lguest_devices" page. */ static void add_lguest_device(struct lguest_device_desc *d) { struct lguest_device *ldev; /* Start with zeroed memory; Linux's device layer seems to count on * it. */ ldev = kzalloc(sizeof(*ldev), GFP_KERNEL); if (!ldev) { printk(KERN_EMERG "Cannot allocate lguest dev %u\n", dev_index++); return; } /* This devices' parent is the lguest/ dir. */ ldev->vdev.dev.parent = &lguest_root; /* We have a unique device index thanks to the dev_index counter. */ ldev->vdev.index = dev_index++; /* The device type comes straight from the descriptor. There's also a * device vendor field in the virtio_device struct, which we leave as * 0. */ ldev->vdev.id.device = d->type; /* We have a simple set of routines for querying the device's * configuration information and setting its status. */ ldev->vdev.config = &lguest_config_ops; /* And we remember the device's descriptor for lguest_config_ops. */ ldev->desc = d; /* register_virtio_device() sets up the generic fields for the struct * virtio_device and calls device_register(). This makes the bus * infrastructure look for a matching driver. */ if (register_virtio_device(&ldev->vdev) != 0) { printk(KERN_ERR "Failed to register lguest device %u\n", ldev->vdev.index); kfree(ldev); } } /*D:110 scan_devices() simply iterates through the device page. The type 0 is * reserved to mean "end of devices". */ static void scan_devices(void) { unsigned int i; struct lguest_device_desc *d; /* We start at the page beginning, and skip over each entry. */ for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) { d = lguest_devices + i; /* Once we hit a zero, stop. */ if (d->type == 0) break; add_lguest_device(d); } } /*D:105 Fairly early in boot, lguest_devices_init() is called to set up the * lguest device infrastructure. We check that we are a Guest by checking * pv_info.name: there are other ways of checking, but this seems most * obvious to me. * * So we can access the "struct lguest_device_desc"s easily, we map that memory * and store the pointer in the global "lguest_devices". Then we register a * root device from which all our devices will hang (this seems to be the * correct sysfs incantation). * * Finally we call scan_devices() which adds all the devices found in the * lguest_devices page. */ static int __init lguest_devices_init(void) { if (strcmp(pv_info.name, "lguest") != 0) return 0; if (device_register(&lguest_root) != 0) panic("Could not register lguest root"); /* Devices are in a single page above top of "normal" mem */ lguest_devices = lguest_map(max_pfn<